This invention relates to drilling machines for working on longer profiles.
More particularly, the invention is concerned with drilling machines of the type suitable for work on more than one side, preferably three sides of elongated steel profiles, and includes a fixed invariable frame comprising a horizontal machine underpart arranged transversely to the longitudinal axis of the workpiece, two vertical side parts attached on the side parts. Three drilling units are provided, each having a drilling spindle, a gear and a motor. The drilling units are shiftable in a plane parallel to the frame. The first drilling unit has a horizontal drilling spindle and is attached to a side part and directed towards one side of the workpiece. The second drilling unit also has a horizontal spindle which is generally directed towards the first drilling unit and is arranged on the opposing side of the one side of the workpiece; and, the third drilling unit has a vertical spindle and is attached to the upper beam.
Drilling machines with a fixed, invariable frame and cradles are known. The first and second drilling units are arranged on each of the two vertical side parts, and each of the drilling units are arranged vertically as a cradle, and on the upper beam a third cradle is arranged. A horizontally mobile spindle sleeve bearing the drilling spindles is arranged in each cradle. The first and second drilling units, which are attached to the side parts, cannot be arranged at any given distance from each other, since the distance of the drilling units from the workpiece is dependent on the limited degree to which the spindle sleeve can be extended outwards; and therefore, very broad profiles can not be worked suitably. When narrow profiles are to be worked, then the spindle sleeves must be extended a long way outwards, and this results in a diminishment of the measuring accuracy of the driller.
Drilling machines are known which are capable of working with a high degree of accuracy on both narrow and broad profiles.
In order to be able to work with a high degree of accuracy on both narrow profiles as well as very broad profiles, the known drilling machines have drilling units provided with horizontal drilling spindles attached to two horizontally movable drilling cradles, which bear an upper beam on their upper side which is not connected with the machine underpart, on which upper beam a further cradle is movably attached for a drilling unit with a vertical drilling spindle. In these known drilling machines, the spindle sleeves are not required to be driven outwards very far for small profiles, as the cradle can move the drilling units near enough to the workpiece. Such cradles, however, are not guided within a closed frame but between the machine underpart and the free upper beam, so that inaccuracies in measuring may occur due to the low stability. Indeed, it was attempted to increase the stability by positioning the drilling units inside the cradle and not on the outside of the cradle so that they lie in the central plane of the machine underpart and the upper beam. However, inaccuracies in measurement can not be avoided completely by doing this, and, moreover, the drilling units are difficult to reach.
Furthermore, in the two known drilling machines, the slide surfaces necessary for the cradle are susceptible to disturbance and are difficult to keep clean. Also, sliding friction, which disturbs positioning, must be overcome for movement of the cradle.
The object of the invention is to provide a drilling machine of simple construction having a low susceptibility to disturbance. This low susceptibility to disturbance permits drilling of very broad workpieces and thereby achieves a high degree of measuring accuracy even with narrow workpieces.